Severance offer, what should I ask for? after 11 years as a bookkeeper

My manager said the package is final, but the letter gives me time to review. I have read a lot of threads here and could not find my exact situation. I do not want to leave money on the table. Should I see a lawyer?

Ask for the offer in writing and do not sign on the spot. A day or two to think is normal.

I asked for two more weeks and a neutral reference. They agreed to the reference and added a week.